HDMIs have come into wide use as a digital interface for transmission of video/audio. The HDMI is arranged for AV devices by adding an audio transmission function and a copyright protection function to DVI which is a connection standard for a PC and a display.
Conventionally, a plurality of cables for each signal of video/audio/control have been used for the connection between devices, however, since the HDMI needs only one cable and control signals correspond to bidirectional transmission, it has also been possible to operate the entire AV system such as a home theater with one remote controller by relaying the control signal to an output apparatus such as an STB (Set Top Box) and a DVD player connected by the HDMI from a monitor.
The basic specification for the standard of the HDMI was established in December 2002 by the standardization organization of HDMI Licensing, LLC (HDMI standard Ver1.0), and a rule for CEC (Consumer Electronics Control) was added as a control protocol for performing control between AV devices in December 2005 (HDMI standard Ver1.2a, refer to Non-Patent Literature 1). After that, although some revisions have been made, description of the CEC will hereinafter be based on the standard after the HDMI standard Ver1.2a and be referred to as the HDMI standard unless otherwise noted.
Note that, terms about the CEC are defined in “2.2 Glossary of Terms” of the HDMI standard, “CEC 2.2 Glossary of Terms” and the like, where one that has an HDMI input terminal is defined as a sink device, one that has an HDMI output terminal and outputs an AV stream is defined as a source device, and one that has an HDMI input terminal and output terminal and inputs/outputs an AV stream is defined as a repeater device.
In the HDMI standard, control between devices using the CEC is defined. According to the CEC, various kinds of control are possible based on individual physical addresses and logical addresses assigned to each device existing on an HDMI network. For example, when reproduction of video is made by depressing a reproduction button, or the like, of a DVD player connected by HDMI while a user views digital broadcast on a television, the television automatically switches to an input connected with the DVD player. Moreover, operation menu displayed on the DVD player, on/off of a power source and the like is able to be operated from a remote controller of the television.
In addition, the HDMI standard prescribes that operation is able to be made even when a maximum of 10 devices including a television are connected, thus it is possible to connect up to nine external devices to a television. When one device compatible with HDMI CEC is connected to the television, it is clear which device is operated from a remote controller, however, when a plurality of devices compatible with HDMI CEC are connected, there is a problem that it is hard to recognize which device is operated from the television using a remote controller of the television.
Hence, it is considered that, when operating of the device compatible with HDMI CEC from the television using the remote controller of the television as described above, by selecting a device actually displaying video on the television as a device targeted for the operation, the operation object device is limited from a plurality of devices. In the HDMI standard, as a CEC message for clearly indicating such a device displaying video on the television, <Active Source> is prescribed. According to this prescription, for example, in a case where a user operates a reproduction button of a DVD player compliant with HDMI CEC, when the DVD player itself is in a state capable of outputting stable video signal (that is, in an active state), the DVD player outputs an AV stream as well as broadcasts <Active Source> indicative of being an active device. Here, the “broadcast” means simultaneous transmission of signal whose transmission destination is not a specific device but all devices. The television and other devices compatible with HDMI CEC to which <Active Source> has been broadcasted switch a route for reproducing the AV stream output from the DVD player. In this way, it is prescribed that in devices compatible with HDMI CEC a device displaying video on TV broadcasts <Active Source> to other devices in a network.
Note that, although an example in a case of operating a reproduction button of a DVD player has been described above, it is similar in the next case. For example, in a case where <Request Active Source> has been broadcasted by other device compatible with HDMI CEC due to a user operation, and when a DVD player is an “active device”, the DVD player broadcasts <Active Source> indicative of itself being an active device. Here, the <Request Active Source> is one of CEC messages defined in the HDMI standard and used for a purpose to inquire about an active device in a route.
However, a method in which an “active device” which has broadcasted <Active Source> becomes as an operation object device has the following problem. To correspond to the CEC itself is optional in the HDMI standard, however, essentially corresponded prescriptions and selectively corresponded prescriptions are mixed in various prescriptions of the CEC, thus posing the following disadvantage.
Assumed is a state where a television includes a plurality of HDMI input terminals, and for example, a device A and a device B that are devices compatible with HDMI CEC are connected to each of the HDMI input terminals. First, it is assumed that a user operates a reproduction button of the device A intending to operate the device A connected to the television. In this case, since the device A is an operable device, the device A broadcasts <Active Source> as described above. That is, at this time, the television and other devices compatible with HDMI CEC having received this are notified that the device A is an “active device”.
Next, it is assumed that the user performs input switching operation of the television intending to operate the device B and selects a connected input of the device B. However, there is a case where the device B does not broadcast <Active Source>, and in such a case, the device A remains as an “active device”. Thus, even when the user performs some operation to the device B, operation signal thereof is transmitted to the device A which is the “active device”. Such disadvantage is caused by that the device B does not correspond to a selectively-corresponded prescription in the HDMI standard.
Even after a user displays video to instruct switching to a device desired to be an operation object, when the switching destination device is not an “active device”, the television does not recognize the device as an operation object device, thus it is impossible to operate the switching destination device from the television.
Contrary to this, even when a device is not an “active device”, there is a method that the television recognizes the device as an operation object device. This method is, regardless of presence/absence of <Active Source>, one in which a device specified by <Set Stream Path> becomes as an operation object device. The <Set Stream Path> is one of CEC messages defined in the HDMI standard, and when an input switching operation is made by a user, transmitted from a television to switch an input path by broadcast.    [Non-Patent Literature 1] High-Definition Multimedia Interface Specification Version 1.2a Supplement 1 Consumer Electronics Control (CEC), Dec. 14, 2005